Campylobacter jejuni is a leading cause of foodborne human gastroenteritis in the United States, with an incidence rate of 13.6 diagnosed cases per 100,000 individuals, though it is predicted that the incidence is much higher, with estimates of approximately 1.3 million cases of campylobacteriosis in the United States annually, arising primarily from poultry, which serves as a natural reservoir for C. jejuni. Campylobacteriosis is characterized by mild to severe, bloody diarrhea, abdominal pain, and fever occurring two to five days following infection, but can also lead to Guillain-Barr syndrome (GBS), a paralytic illness resulting from the immune system attack on the peripheral nervous system. Research to uncover factors of C. jejuni that contribute to development of human campylobacteriosis has been hindered by lack of an animal model that replicates the clinical features of human disease. The widely used chicken model is not a disease model, as chickens are a natural reservoir for Campylobacter species. Development of animal models that mimic human disease has centered on immunodeficient mice, including MyD88, IL-10 or NF-kB mutants, or more complex experiments where the murine gut microbiota is replaced with a human gut microbiota after antibiotic treatment. These are poor models of human disease as colonization does not result in clinical signs consistent with human infection, or because colonization leads to a long-term, persistent infection, also unlike what is observed in humans. In contrast, infection in young ferrets closely mimic human infection, including development of bloody diarrhea and resistance to disease upon re-infection. Little is understood, however, about host and microbial mechanisms that underlie campylobacteriosis in the ferret model. For this exploratory proposal, a broad approach to uncover physiological and genetic factors contributing to C. jejuni infection in ferrets will be taken, combining transcriptomics, genetics, metagenomics, and metabolomics. This approach has been successful at uncovering significant knowledge regarding C. jejuni commensalism in the chicken gastrointestinal tract, including the discovery of colonization determinants, new regulatory elements and potential non-coding small RNAs. Adopting this systems strategy to study a disease model, with subsequent comparative analysis of the chicken commensal findings, will provide unprecedented insight into important host-pathogen interactions relevant to C. jejuni pathogenicity. The proposed work for this proposal has the following two aims: Specific aim 1. Identify C. jejuni determinants and correlates of pathogenicity in the ferret model using transcriptomic and genome-wide mutagenesis studies -genes identified as critical for pathogenicity in the ferret will be examined in a chicken model to assess their rol in commensal colonization without inflammation and pathogenicity signs Specific aim 2. Determine the ferret response to Campylobacter jejuni infection using transcriptomic, metagenomic, and metabolomic studies.